1. Field of the Invention
The present invention relates to orthopedic devices for the stabilization and control of a human knee joint which has been injured. More particularly, the invention relates to a hinge for a knee brace which will permit the user a relatively high degree of freedom in the use of the bones while, at the same time, permitting control of the knee joint so as to optimize healing and stability.
2. Description of the Related Art
Devices for adding support and strength to the knee joint, such as that disclosed in U.S. Pat. No. 4,802,466, which is hereby incorporated by reference, have been known for decades and have taken many different forms. While substantially all of these devices have been purported to have mechanical joints designed to produce a smooth articulation of the mechanical joint that is matched to the behavior of the natural human knee joint, very few have, in fact, done so since most known devices have apparently taken for granted that the relative movement of the femur and tibia is a rotation about a single center of rotation, typically in the center of the knee. However, studies have shown that a single pivot movement does not emulate the relative movement of the femur and tibia, and that to do so a mechanical joint must produce a rearward movement of the tibia relative to the femur throughout the full flexion range of the tibia, or for whatever angle may be traversed as limited by the injury or natural limitations of the knee brace wearer.
Attempts have been made in prior art devices to more closely mimic the natural movement of the human knee joint such as the devices disclosed in U.S. Pat. Ser. Nos. 4,723,539, 4,773,404 and 4,890,607. In each of these patents, a multiaxis controlled motion knee orthosis is disclosed having a joint that is designed to constrain the tibia to slide rearwardly relative to the femur for a predetermined distance throughout an initial range of flexion of the knee from a straight leg position, and, beyond that initial range of flexion, to rotate relative thereto along a predetermined arcuate path irrespective of the loading applied to the joint by the leg of the wearer.
Therefore, in each of these devices, the tibia slides rearwardly such that its axis of rotation is constantly changing only for an initial portion of the full range of flexion of the knee. After this initial portion of flexion movement has been obtained, the tibia no longer slides rearwardly, and instead rotates about a single axis throughout the remaining portion of flexion movement. Accordingly, while these devices more closely operate like a natural knee joint as compared to the single center of rotation devices, they are still deficient in mimicking the natural knee joint in which the tibia continually slides rearward during the entire flexion movement producing a constantly changing axis of rotation of the tibia relative to the femur.
Moreover, the above devices fail to take into account the fact that during the full range of flexion motion, the medial side of the knee first moves anteriorly prior to moving posteriorly, while the lateral side of the knee continually moves posteriorly during the full range of flexion movement.